The In-In formalism has been used to compute radiation reaction effects at 2.5PN in [1]}, at 3.5PN in [2]}. It has also been used for tail at 4PN in [3]}[4]}[5]}, at 5PN in [6]}, for tail of tail effects up to 7PN order in [7]}, and for memory effects up to 5PN in [6]}. For reviews of In-In formalism in classical systems one can consult [9]}, [10]}.
